Process for the production of unsaturated acids and esters

ABSTRACT

Compositions of the empirical formula: 
     
         Mo.sub.12 P.sub.0.1- Te.sub.0.01-2 M.sub.0.1-3 M&#39;.sub.0.01-3 X.sub.a 
    
      O b   
     where 
     M is at least one of K, Rb and Cs; 
     M&#39; is at least one of Cu and V; 
     X is at least one of Ba, Zn, Ga, Nb, Cd, Ti, Ca, Bi, Mg, Ta, Zr, Ce, Ni, Co, Cr, Fe and Tl when a&gt;0; 
     a is a number of 0 to about 2; and 
     b is a number that satisfies the valence requirements of the other elements present, 
     are excellent catalysts for the oxydehydrogenation of saturated, lower aliphatic acids and esters to the corresponding unsaturated acids and esters.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to catalysis. In one aspect, the inventionrelates to the catalytic oxydehydrogenation of saturated, loweraliphatic acids and esters to the corresponding unsaturated acids andesters while in another aspect, the invention relates to the manufactureof methacrylic acid by the oxydehydrogenation of isobutyric acid with aheteropolyacid, tellurium-containing catalyst.

2. Description of the Prior Art

U.S. Pat. No. 4,061,673 teaches the manufacture of methacrylic acid bythe oxidative dehydrogenation of isobutyric acid using a heteropolyacidconsisting of molybdenum, tungsten, vanadium, phosphorus and oxygen. Thecatalyst is supported on a carrier having a silicon dioxide content ofat least 70% and a water absorbability of at least 60%.

U.S. Pat. No. 3,917,673 teaches the synthesis of unsaturated, loweraliphatic acids and esters by the catalytic oxidative dehydrogenation ofthe corresponding saturated acids and esters. The catalyst is thecalcined residue of a mixture of bismuth oxynitrate, iron phosphate andlead phosphate.

Other processes and catalysts are known for the oxidativedehydrogenation of isobutyric acid and similar materials to methacrylicacid and similar products. Representative of these include DT No.2,438,464, BE No. 848,300 and Japanese patent applications Nos.3,082,720, 2,105,112, 2,105,113, 1,118,718, 2,039,622 and 2,031,018.

Heteropolyacid, tellurium-containing catalysts are known to be usefulfor the manufacture of methacrylic acid from methacrolein. See forexample JAP application No. 2,051,316, GB No. 1,478,828 and NL No.7602-438.

SUMMARY OF THE INVENTION

According to this invention, saturated, lower aliphatic acids and estersare oxydehydrogenated to the corresponding unsaturated acids and estersby use of a catalyst of the empirical formula:

    Mo.sub.12 P.sub.0.1-3 Te.sub.0.01-2 M.sub.0.1-3 M'.sub.0.01-3 X.sub.a O.sub.b                                                   (I)

where

M is at least one of K, Rb and Cs;

M' is at least one of Cu and V;

X is at least one of Ba, Zn, Ga, Nb, Cd, Ti, Ca, Bi, Mg, Ta, Zr, Ce, Ni,Co, Cr, Fe and Tl when a>0;

a is a number of 0 to about 2; and

b is a number that satisfies the valence requirements of the otherelements present.

Use of these catalysts give good per pass conversions of the saturatedacids and esters and good selectivity to the unsaturated products.

DETAILED DESCRIPTION OF THE INVENTION

The saturated, lower aliphatic acids and esters of this invention are ofthe structural formula: ##STR1## where R-R'" are independently hydrogenor a C₁ -C₄ alkyl radical. Preferred starting materials are the acids(R'" is hydrogen) while more preferred starting materials are acidswhere R and R' are hydrogen. Isobutyric acid (R, R' and R'" are eachhydrogen and R" is methyl) is especially preferred. These lower,saturated acids and esters can contain inert substituents, i.e.,substituents that are essentially nonreactive with the processreactants, catalysts and products at process conditions, but arepreferably free of substituents.

Molecular oxygen can be used in either a relatively pure form or dilutedby one or more carrier gases. For reasons of economy and convenience,the molecular oxygen is usually introduced as air.

As is evident from formula I, the catalytic composition of thisinvention is at least a six element material, i.e., a materialcontaining molybdenum, phosphorus, tellurium, alkali metal (M), copperand/or vanadium and oxygen all in designated, proportional amounts.Preferably, the subscript value of phosphorus in formula I is about 0.8to 1.5, of tellurium about 0.1 to 1, of alkali metal (M) about 0.15 to2, and of copper and/or vanadium (M') about 0.2 to 2.5.

Certain catalysts of this invention are those where a is greater than 0,typically a number of about 0.01-2. These catalysts contain one or morepromoter elements X, typically zinc, cadmium, bismuth, titanium orbarium.

As is taught by formula I, certain of the components can be combinationsof two or more elements, e.g., M' can be a combination of copper andvanadium. In such instances, the subscript value represents the sum ofthe elements (e.g. for M', the sum of copper and vanadium is a number ofabout 0.01 to 3). Generally M and X each represent but a single element.

One preferred class of catalytic compositions is seven element orcomponent (including oxygen) catalysts where M is rubidium or potassium,and M' is a combination of copper and vanadium.

The exact structure or element arrangement of these catalysts is notknown but the metal and phosphorus components are present in the form oftheir oxides, acids or oxyacid complexes. However, the compositions offormula I are known not to be a mere physical mixture of theircomponents but rather unique compositions where the individualcomponents are chemically and/or physically bonded to one another.

The catalytic compositions of this invention can be used either in the100% active form or in a diluted form, i.e. supported or unsupported.Suitable support materials include silica, titania, alumina, zirconia,silicon carbide, boron, various phosphates, etc., with low surface area(about 1 m² /g) alumina being a preferred support material. If a supportis used, the catalytic composition is generally present in an amount ofat least 20 weight percent, based on the combined weight of the supportand the catalytic composition, and preferably in an amount of at leastabout 30 weight percent.

The catalytic compositions of this invention can be prepared in any oneof a number of different methods, the particular method employed being amatter of convenience. Typically, the catalysts are prepared by mixingthe appropriate catalyst ingredients in the proper proportions in anaqueous mixture, drying the resulting aqueous slurry with or without areducing agent, and calcining the product. The ingredients can be addedin any order during the preparation procedure but certain orders arepreferred, particularly the mixing of the metallic ingredients prior tothe addition of phosphorus (generally in the form of phosphoric acid).The ingredients employed can be the oxides, halides, nitrates, acetatesor other salts of the particular metals or elements added, andparticularly preferred is the use of water soluble salts of the metalcomponents. If a support is used, the material comprising the supportmay be incorporated into the catalyst along with the other ingredientsor the catalyst composition may be coated and/or impregnated onto orinto a core. After the catalyst ingredients have been combined to forman aqueous slurry, the slurry is taken to dryness and the dried solidobtained is heated in the presence of air, nitrogen, nitric oxide or amixture of any two or more of these gases at temperatures between about300° and 420° C. This calcination can take place outside the catalyticreactor or an in situ activation can be utilized. Other methods ofpreparation are known in the art.

The process of this invention is conducted in the vapor phase. Thevaporous, saturated starting material is contacted with the solidcatalyst in the presence of molecular oxygen. Any temperature at whichthe starting material is vaporous can be employed but preferably thetemperature is between about 280° and 380° C. Likewise, any pressure atwhich the starting material is vaporous can be employed and thesepressures range from subatmospheric to superatmospheric. Typically,autogenous pressure is employed. The molar ratio of oxygen to saturatedacid or ester can also vary widely with typical molar ratios rangingfrom about 5 to about 1. As indicated earlier, the feed mixture (acidand/or ester plus oxygen) can be diluted with a carrier gas, such asnitrogen, water vapor, carbon dioxide, helium or argon. Sufficientcatalyst is employed to insure adequate opportunity for the reactionfeed to contact the catalyst surface. Contact time can range from afraction of a second to several hours or more with a preferred contacttime ranging from about 0.1 sec to about 10 sec.

The products of this invention are of the structural formula: ##STR2##where R-R'" are as defined for formula II. These products have a widerange of utility particularly in the manufacture of films, plasticsheets and paints.

The following example is illustrative of a specific embodiment of thisinvention.

SPECIFIC EMBODIMENTS Catalyst preparation

The catalyst was prepared by dissolving, with stirring, ammoniumheptamolybdate in distilled water and heating the resulting solution to30°-35° C. While continuously stirring the solution and maintaining thetemperature, rubidium hydroxide was added. After 15 min, copper acetateand ammonium metavanadate solutions were added followed by addition of atellurium trichloride/hydrochloric acid solution. The resulting slurrywas then heated to about 70° C. for two hours. Phosphoric acid (H₃ PO₄)was the last material added after which stirring and heating wascontinued for 30 min and the pH of the slurry was adjusted to 5.6. Themixture was then evaporated into a thick paste and the catalystprecursor dried in an oven at 110°-120° C. The resulting powder wascoated onto 1/8 in. Alundum® spheres (alumina support) so that thepowder coating (i.e. the catalyst) constituted about 35 weight percentof the coated spheres. The catalyst composition had the empiricalformula:

    Mo.sub.12 P Rb Te.sub.0.5 Cu.sub.0.25 V.sub.0.5 O.sub.b

Process Procedure and Conditions

The reaction was conducted in a 20 cc downward-flow, fixed-bed reactor.After the catalyst was introduced into the reactor, it was exposed toone hour of air flow (no feed) at 370° C. followed by one hour at 345°C. with air flow plus feed before the temperature was dropped to thereaction temperature, 329° C. After a short stabilization period, a 15min run was conducted. The VVH (volume of isobutyric acid per volume ofcatalyst per hour) was about 51.6, the air/isobutyric acid mole ratiowas about 4.6 and the water/isobutyric acid mole ratio was about 25.3.The off-gas rate was measured with a soap-film meter and the off-gascomposition was determined at the end of the reaction with the aid of aPerkin-Elmer 154 gas chromatograph. At the end of the reaction, theentire scrubber liquid was diluted with distilled water to about 100 g.A weighed amount of methanol was used as an internal standard in a 20 galiquot of the dilute solution. A one microliter sample was thenanalyzed in a Varian Model 3700 gas chromatograph fitted with a flameionization detector and a Chromsorb 107 column, 60/80 mesh. The splitbetween methacrylic, isobutyric and acetic acids was determined from thegas chromatographic analysis.

The reactor effluent analyzed as 64.1% methacrylic acid for aselectivity to methacrylic acid of 67.4%.

Although this invention is described by the above example, this exampleis for the purpose of illustration only and it is understood thatvariations and modifications can be made by one skilled in the artwithout departing from the spirit and scope of the invention.

The claimed invention is:
 1. A vapor-phase process for the production ofa compound of the formula: ##STR3## the process comprising contacting inthe presence of molecular oxygen a compound of the formula: ##STR4##where R-R'" are independently hydrogen or a C₁ -C₄ alkyl radical, with acatalytic amount of a catalyst of the empirical formula:

    Mo.sub.12 P.sub.0.1-3 Te.sub.0.01-2 M.sub.0.1-3 M'.sub.0.01-3 X.sub.a O.sub.b                                                   (I)

where M is at least one of K, Rb and Cs; M' is a combination of Cu andV; X is at least one of Ba, Zn, Ga, Nb, Cd, Ti, Ca, Bi, Mg, Ta, Zr, Ce,Ni, Co, Cr, Fe and Tl when a>0; a is a number of 0 to about 2; and b isa number that satisfies the valence requirements of the other elementspresent.
 2. The process of claim 1 where M is K or Rb.
 3. The process ofclaim 2 where a>0.
 4. The process of claim 3 where X is at least one ofZn, Cd, Bi, Ti and Ba.
 5. The process of claim 3 where X is at least oneof Zn, Bi and Cd.
 6. The process of claim 2 where a is
 0. 7. The processof claim 6 where the subscript value of P in formula I is about 0.8 to1.5, of Te about 0.1 to 1, of M about 0.15 to 2, and of M' about 0.2 to2.5.
 8. The process of claim 7 where the catalyst is unsupported.
 9. Theprocess of claim 7 where the catalyst is diluted with a support.
 10. Theprocess of claim 9 where the support is a low surface area alumina. 11.The process of claim 10 where the compound of formula II is isobutyricacid.